1 synthesis,functionalization,andcharacterization ...nanomaterials, including fullerenes, carbon...

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1Synthesis, Functionalization, and CharacterizationJianxun Xu, Xing Lu, and Baowen Li

1.1Introduction

Recent years have witnessed tremendous development in the studies of carbonnanomaterials, including fullerenes, carbon nanotubes (CNTs), and graphene.These carbon nanomaterials solely comprise sp2 carbon atoms, which formconjugated six-membered rings fused together with various numbers of five-membered rings. These novel materials, which exhibit unique structures andproperties, are expected to be useful in many fields.

To achieve the proposed applications, it is of primary importance to synthesizethese nanomaterials with defined structures in reasonable production yield. At thesame time, it is always required to further modify their surface properties to opti-mize the interface environment where they function. The fine structure and thesurface properties are critical for their biological effects. And, it is actually impor-tant to identify the comprehensive structure parameters and surfacemodificationsfor their toxicological evaluations and understanding the related mechanisms. Inthis chapter, we present the basic concept and the latest achievements in the syn-thesis of carbon nanomaterials and their functionalization, especially related tobiological purposes. The state-of-the-art characterization methods are also criti-cally reviewed.

1.2Fullerenes and Metallofullerenes

There have been a tremendous amount literature describing the synthesis, charac-terization, structures, and properties of empty fullerenes. As a result, we will onlyfocus on the achievements in the recent studies of endohedral metallofullerenes(EMFs), which are hybrid molecules formed by the encapsulation of metallicspecies into the fullerene cages in the following contexts.

Biomedical Applications and Toxicology of Carbon Nanomaterials, First Edition.Edited by Chunying Chen and Haifang Wang.© 2016 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2016 by Wiley-VCH Verlag GmbH & Co. KGaA.

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2 1 Synthesis, Functionalization, and Characterization

Anode

(a) (b)

He

Cathode

Cooling water

In

Out

Vacuum pump

Figure 1.1 (a) An arc discharge reactor used to synthesize EMFs and (b) its schematicillustration.

1.2.1Synthesis and Purification

1.2.1.1Synthesis

The synthesis of empty fullerenes can be achieved rather easily via such methodsas initial laser ablation, then arc discharge, and finally combustion of aromaticorganic molecules even under ambient conditions. However, to produce EMFs,harsher conditions are always required to evaporate the metals into the gas phase.As such, only laser ablation and arc discharge approaches are effective.

Smalley and colleagues made the first attempt by using laser ablation equip-ment. A composite graphite disk doped with lanthanum oxide was irradiated withlaser in a quartz tube under an inert atmosphere. The tube was heated to a temper-ature higher than 800 ∘C in order to ensure the formation of fullerenes and EMFs[1–3].

This is the most powerful and convenient method for EMF production(Figure 1.1). By allowing N2 or NH3 into the chamber, or by adding somenitrogen-containing compounds into the graphite rod, metal nitride clusterEMFs are readily obtained [4, 5]. EMFs containing a metal oxide cluster (Sc4O3)[6], a metal sulfide cluster (Sc2S) [7], or even a metal cyanide cluster (Sc3NC)have been synthesized by introducing the corresponding heterogeneous additivesinto the reactor.

1.2.1.2Purification

Extraction Solvent extraction is the most common method and frequently used inthe first step of fullerenes separation from soot. Generally, 1,2,4-trichlorobenzene(TCB) shows the highest affinity toward the fullerene species. Alternatively,

1.2 Fullerenes and Metallofullerenes 3

1,2-dichlorobenzene (ODCB), chlorobenzene, toluene (xylene, benzene), andCS2 are also commonly used to extract fullerenes and EMFs [8–10].

On the other hand, electrochemical methods were also used for the extrac-tion of insoluble EMFs. The insoluble species can be made soluble by alteringthe electronic properties of these insoluble species. Diener and Alford made thefirst attempt, and obtained a mixture of insoluble, small-bandgap fullerenes suchas C74, Gd@C60, and Gd@C74 by electrochemical reduction of the sublimate ofGd-containing soot [11]. In addition, some insoluble EMFs were extracted afterincreasing the solubility via chemical derivatization. For example, upon extractionwith 1,2,4-trichlorobenzene of La-containing soot, some insoluble species suchas La@C2n (2n= 72–82) were functionalized by the trace dichlorophenyl radicalsgenerated during refluxing [12–16].

HPLC Separation Complete separation of EMFs has been accomplished only byhigh-performance liquid chromatography (HPLC) [17–19], which has proven tobe the most powerful and frequently used technique for the separation of EMFs.The HPLC technique utilizing different modified HPLC columns can even affordthe separation of structural cage isomers of various EMFs. Five complementaryHPLC columns are available commercially: PYE, PBB, NEP, Buckyprep, andBuckyprep M.

Non-HPLC separation Electrochemical studies of EMFs have indicated that theirredox potentials are quite different from those of empty fullerenes, so electro-chemical methods can be efficiently used for separating EMFs from the latter. In2003, Bolskar and Alford designed a separation protocol based on the electro-chemical as well as chemical oxidation of EMF extracts by AgPF6, AgSbCl6, andtris(4-bromo-phenyl)aminium hexachloroantimonate [20].

Moreover, the “SAFA” (stir and filter approach) was proposed by Stevensonet al. [21, 22]. Without using any chromatography equipment, the authors usedcyclopentadienyl and amino-functionalized silica to selectively bind contaminantfullerenes (empty fullerenes and non-nitride clusterfullerenes) and claimed toobtain the purified nitride clusterfullerenes under optimum conditions [21].This method could also be used to separate Sc3N@C80-Ih and Sc3N@C80-D5hisomers [22].

1.2.2Chemical Functionalization

1.2.2.1Carbene ReactionCarbene reaction is used frequently to functionalize many different kindsof EMFs; this is mainly due to its highly selectivity. For example, throughphotoirradiation or even heating, reactions of M@C2v-C82 (M = La, Y, Pr, Gd,etc.) with 2-adamantane-2,3-[3H]-diazirine (AdN2) were conducted and twomonoadducts of M@C2v-C82 were obtained [23]. The single-crystal results


(a) (b) (c) (d)

(e) (f) (g) (h)

Figure 1.2 Ortep drawings of (a) Y@C82 –Ad, (b) Yb@C84Ad, (c) La2@C80 –Ad,(d) La2@C80 –NTrt, (e) Ce2@Ih –C80 –(Mes2Si)2CH2, (f ) Sc3C2@C80 –CH2C6H5,(g) La@C82 –CBr(COOC2H5)2, (h) Sc3N@C80 –C6H4.

(Figure 1.2a) revealed that the addition always took place on those carbon atomsnear the metal atom. Similar reaction of dimetallofullerenes M2@C80 (M=La,Ce) were carried out by Akasaka’s group. The single-crystal X-ray structure(Figure 1.2c) analysis of monoadduct La2@C80Ad confirmed that two La atomswere interestingly collinear with the spiro carbon of the Ad group and thedistance between La atoms is increased [24]. Recently, the carbene reaction hasbeen used to investigate the chemical properties of divalent EMFs. Reaction ofYb@C80 with AdN2 reported by Lu in 2013 resulted in the first derivative of adivalent metallofullerene. Only one isomer was obtained, indicating the highregioselectivity of this reaction [25]. Yb@C84 (Figure 1.2b) was used to reactwith AdN2 in the same year. Theoretical calculations suggest that the addition ofdivalent EMFs is mainly driven by the release of the local strains of cage carbonsrather than by charge recombination, which is always prominent due to theaffinity of typical trivalent EMFs [26].

1.2.2.2Bingel–Hirsch ReactionThe Bingel–Hirsch reaction is one of the famous nuclophilic reactions in fullerenechemistry. The reactions of diethyl bromomalonate with metallofullerenes in thepresence of 1,8-diazabicyclo[5.4.0]-undec-7ene (DBU) are extremely aggressive,so it is always used to synthesize various adducts. Surprisingly, Akasaka obtained


a singly bonded monoadduct of La@C82(La@C82CBr(COOC2H5)2) (Figure 1.2g)by means of the Bingel–Hirsch reaction [27].

1.2.2.3Prato Reaction

Many investigations of Prato reaction of metallofullerenes indicate that changingthe substituted group of aldehydes is a very efficient approach to obtain met-allofulleropyrrolidines with different branched chains. This method is widelyused to introduce functional groups for further photophysical studies. The firstPrato reaction of EMFs was carried out by adding azomethine ylide into La@C82solution. Two major endohedral metallofulleropyrrolidines, a monoadduct and abisadduct of La@C82, were isolated with HPLC, which suggested that the reactionis regioselective to some extent. A special Prato reaction of M2@C80 (M = La,Ce) with 3-triphenylmethyl-5-oxazolidinone (NTrt) was reported by Akasaka’sgroup; the [6,6]- and [5,6]-adducts resulted were and characterized. The X-raycrystallographic analysis of the [6,6]-adduct (Figure 1.2d) confirmed that themetal atoms are fixed, which is opposite of the random circulation in pristineLa2@C80 [28].

1.2.2.4Bis-Silylation

Bis-silylation of La@C2v–C82 reported by Akasaka et al. in 1995 was the firstexohedral chemical functionalization of metallofullerenes [29]. Afterward, theysucceeded likewise in the bis-silylation of M@C2v–C82 (M = Gd, Y, Ce) andM@Cs-C82 with disilirane through a photochemical or thermal pathway [30]. Sim-ilar works of di-EMFs such as M2@C80 (M= La, Ce) (Figure 1.2e) were conductedby Akasaka. In 2006, the reaction of trimetallic nitride-templated endohedralmetallofullerene (TNT EMF) Sc3N@C80 with 1,1,2,2-tetramesityl-1,2-disiliraneunder photoirradiation was carried out. Both 1,2- and 1,4-cycloadducts weresuccessfully isolated and completely characterized by NMR measurement andsingle-crystal X-ray structure analysis.

1.2.2.5Diels–Alder Reaction and Benzyne Reaction

Cyclopentadiene (Cp) and 1,2,3,4,5-pentamethylcyclopentadiene (Cp*) were usedto participate in the [4 + 2] reaction of La@C82. Interestingly, Diels–Alder reac-tions of La@C82 with Cp was reversible even at 298 K, which was proved throughHPLC. X-ray analysis of La@C82Cp* showed that 60% of the monoadduct formeda dimer in the solid state [31]. Benzyne reaction of La@C82 was undertaken by Luin 2010, and the X-ray crystallographic structure analysis of the adduct showedthat two benzyne moieties were attached to the highly pyramidized sectionand NO2 was unexpectedly linked to cage [32]. Later on, two similar benzynereactions of Sc3N@C80 (Figure 1.2h) were reported by Echegoyen and Wang in2011. Besides the typical cycloadditions above, some uncommon cycloadditions


of metallofullerenes such as radical malonate addition, azide addition, zwitterionaddition, carbosilylation, so on, were investigated as well to some extent [30].

1.2.2.6Singly Bonded AdditionThe thermal reaction of La@C82 with 3-triphenylmethyl-5-oxazolidinone(NTrt) reported by Akasaka in toluene afforded the benzyl monoadductsLa@C82(CH2C6H5), Surprisingly, the same monoadducts were also obtained bythe photoirradiation of La@C2v–C82 in toluene without NTrt [33]. In 2008, Dornobtained a dibenzyl adduct M3N@C80(CH2C6H5)2 (M = Sc, Lu) by photochem-ical reactions of M3N@C80 (M = Sc, Lu) with benzyl bromide, and confirmed thestructure of 1,4-dibenzyl adduct of M3N@C80 (M = Sc, Lu) by X-ray crystallo-graphic analysis [34]. Recently, photochemical reaction of Sc3C2@C80 with benzylbromide was undertaken by Lu, in 2014. X-ray structure analysis (Figure 1.2f )demonstrated that the cluster configuration in EMFs was highly sensitive to theelectronic structure, which is tunable by exohedral modification [35]. Anothertypical singly bonded addition of EMFs is perfluoroalkylation. Perfluoroalkyla-tion of metallofullerens, which is a special solid–solid reaction, prefers to affordvarious multiadducts. CH3I and Ag(CF3CO2) are widely used as reagents forthe perfluoroalkylations of EMFs. Reactions of Sc3N@C80 were the most inves-tigated because of the less selectivity of perfluoroalkylation and relatively largeamount of Sc3N@C80. After persistent efforts, single crystals of the multiadductSc3N@C80(CF3)n (n= 14, 16) were obtained by Yang and coworkers [30]

1.2.2.7Supramolecular Complexes of EMFsSupramolecular complexes based on metallofullerenes with macrocycles ororganic donors have been investigated because of its attractive electron transferbehavior. In 2006, Akasaka and colleagues synthesized complexes of La@C82 with1, 4, 7, 10, 13, 16-hexaazacycloctadecane. The complexes, which precipitate intoluene, are soluble in polar solvents. According to this phenomenon, they suc-cessfully separated metallofullerenes from soot extracts selectively [36]. Anotherorganic donor, N ,N ,N ′N ′-tetramethyl-p-phenylenediamine (TMPD), was alsoused to form complexes with La@C82; the characterization with spectroscopy andESR confirmed the reversible intermolecular electron transfer system at completeequilibrium in solution and the formation of stable diamagnetic/paramagneticanions of La@C82 and radical anions of the donor, respectively [37].

1.2.3Characterization

1.2.3.1Synchrotron Radiation Powder Diffraction (SRPD)/Rietveld/MEMThis method is the earliest to confirm EMFs [38]. In 1995, Takata et al. reportedthe MEM maps of Y@C82 and C82 and confirmed that the metal atom is indeed


encapsulated inside the fullerene cage [38]. Thereafter, the structures of numerousEMFswere determined similarly, such as those of Sc@C82, La@C82, andY2C2@C82[39–41]. This experiential strategy is not always reliable because several erroneousstructures have been assigned using this method [42, 43].

1.2.3.2Nuclear Magnetic Resonance (NMR) SpectroscopyNMR spectroscopy was also used to characterize structures. The cage structuresof many trivalent EMFs have been established, especially those of M@C82, show-ing that both C2v(9)-C82 and Cs(6)-C82 cages are favorable, with the former beingmuch more stable. Furthermore, using the two-dimensional incredible naturalabundance double quantum transfer experiment (INADEQUATE), bond connec-tivities among nonequivalent cage carbons were also modeled in cases where theNMR spectrum was sufficiently clear [44, 45]. Recently, the signals from the inter-nal C2 unit of carbide cluster EMFs were detected with NMR spectrometry using13C-enriched samples. For the Sc2C2 cluster, which is frequently encountered incarbide cluster EMFs, peaks of the C2 unit are observed between 220 and 260 ppm,but the corresponding signal of the C2 motif in the Sc3C2@Ih(7)-C80 anion wasshifted downfield to 328 ppm [46–49]. For divalent EMFs, di-EMFs, and clusterEMFs, which are all diamagnetic species, direct NMR measurements are valid forestablishing their structures [50–52].

1.2.3.3Theoretical CalculationCalculations can predict the relative stabilities of EMF by considering the chargetransfer from the encapsulated metals to the carbon cage [48, 53]. A “maximumpentagon separation rule” proposed by Poblet and coworkers stated that the pen-tagonal carbon rings on the fullerene cage tend to accumulate negative chargestransferred from the internal metallic species. Consequently, they are separatedto the greatest degree over the cage, engendering the maximum separation of thepositively charged internal metal cations.

1.2.3.4Single-Crystal X-ray Diffraction CrystallographyIt is the most reliable solution to molecular structures. The EMF canform neat co-crystals with metal porphyrins: MII(OEP) (M=Ni, Co etc.,OEP= 2,3,7,8,12,13,17,18-octaethylporphyrin dianion) as the eight alkyl groupsof MII(OEP) wrap the spherical molecule. Balch and colleagues have also obtainedthe structure of Kr@C60, indicating that the inert gas molecule is at the centerof the cage [54]. In contrast, the single metal in mono-EMFs always departsfrom the center of the cage, either approaching closely to a hexagonal carbonring for rare-earth metals or over a carbon bond for alkali metals, for example,M@C3v(134)-C94(M=Tm, Ca) [55]. In large cages, it is also possible for thesingle metal to move even at low temperatures (e.g., Sm@C90 isomers) [56]. It isnoteworthy that the crystal of Li+@C60 was obtained by co-crystallization with


its counter anion, [SbCl6]−, instead of metal porphyrin [57]. Furthermore, it wasfound in a recent study that the solvated Sc3N@C80 are nicely ordered in thecrystal lattice, providing new insight into the structures of “pristine” EMFs [58].

1.2.3.5OthersIn addition to the methods that can be viewed as direct solutions to themolecular structure of EMFs, means such as infrared spectroscopy, Ramanspectroscopy, absorption spectroscopy, electrochemical spectroscopy, and evenhigh-resolution tunneling electronic microscopy (HRTEM) have all been used tocharacterize EMFs.

1.2.4Questions and Future Directions

The development and structural recognition of fullerenes and metallofullereneshave a long way to go. The availability of EMFs is much less than sufficient for sci-entific research or practical application. Except for Sc3N@C80, other EMF speciesyielded less using the arc discharge method, and are more difficult to separate,because of the numerous structural isomers and low stability. As a result, morepowerful synthetic methods and more efficient separation process are urgentlyneeded to increase the availability of EMFs.

Practical applications of these fascinating materials also demand detailed explo-ration. Because of the presence of the metallic species, which are the mainstay ofmany novel electronic, magnetic, and optic applications, every detail of the func-tions of both the fullerene cage and the metallic core must be investigated.

1.3Carbon Nanotubes

CNTs, including single-walled carbon nanotubes (SWCNTs) and multi-walledcarbon nanotubes (MWCNTs), can be imagined as cylinders by rolling up hexag-onal carbon sheets. The diameter and the chirality of a SWCNT can be definedin terms of its chiral vector (m, n), which determines the direction of rollingthe carbon sheet, as illustrated in Figure 1.3. It is fantastic that SWCNTs withdifferent (m, n) values exhibit different electrical (metallic or semiconducting)and optical properties in spite of the same chemical composition and bondingbehaviors [59].

CNTs were probably observed for the first time using transmission electronmicroscopy (TEM) in the 1970s. But, only after Iijima et al.’s reports on their dis-covery and structural characterizations on MWCNTs in 1991 and SWCNTs in1993, researchers around the world started to intensively study this kind of newmaterials, which have been proven to possess outstanding mechanical, thermal,optical, and electrical properties [59–61]. Various potential applications of CNTs

1.3 Carbon Nanotubes 9

(0, 0) (1, 0) (2, 0) (3, 0) (4, 0) (5, 0) (6, 0) (7, 0) (8, 0) (9, 0) (10, 0) (11, 0)

(1, 1)

(2, 2)

(3, 3)

(4, 4)

(5, 5)

(6, 6)

a1

a2

Armchair

Zigzag

SWCNT (10, 0)

Figure 1.3 A carbon nanotube can beregarded as a cylinder obtained by rollingup a graphene sheet. The vector conven-tion is used to define the points in the

graphene lattice. The illustrated SWCNT(10, 0) is formed by superimposing the point(10, 0) with (0, 0) in the graphene sheet,which is a zigzag tube.

are expected for composites, flat panel displays, electronic nano-devices, sensors,functional probes, drug delivery systems, and so forth [62–67].

1.3.1Synthesis

The widely used methods to synthesize CNTs are arc discharge, laser ablation, andchemical vapor deposition (CVD).

1.3.1.1Arc Discharge Method

An arc discharge can be used to produce various carbon nanomaterials, includingfullerenes, CNTs, and carbon nanohorns. It is an effective way to synthesize high-quality CNTs having different structural features. The SWCNTs and MWCNTsobserved by Iijima in his pathbreaking work were actually obtained by meansof arc discharge. The facility is very similar to that used to produce fullerenesdescribed previously (Figure 1.1). Under optimal conditions of arcing between twohigh-purity graphite electrodes, MWCNTs can be synthesized. SWCNTs can begenerated by arc discharge only when suitable metal catalysts are used, includ-ing Fe, Co, Ni, Pt, and Rh [61, 68, 69]. CNTs produced by arc discharge havefew structural defects, which helps in preserving the unique properties of CNTs.Meanwhile, it also causes problems to handle these CNTs in wet processes. Forexample, it is difficult to disperse such CNT powders well in the aqueous phasewhen researchers aim to use CNTs for biological applications.


1.3.1.2Laser Ablation MethodLaser ablation is another method developed for CNT synthesis at the early stageof studies on carbon nanomaterials. Carbon evaporated from high-purity graphitesource under high-power YAG laser irradiation can form MWCNTs at 1200 ∘Cin an Ar or a N2 atmosphere [70]. When metal catalysts (Co–Ni) were mixedinto the graphite target, SWCNT bundles were synthesized [71]. On the otherhand, spherical aggregates of single-walled carbon nanohorns were obtained inthe absence of any catalyst at room temperature [72, 73]. Currently, laser ablationmethod is not widely adopted for CNT synthesis because of the necessity of high-power lasers and high-purity graphite.

1.3.1.3CVDMethodMany research groups and commercial manufacturers are using CVD for thesynthesis of CNTs, which is a versatile and economic method to produce differenttypes of CNTs and graphene (discussed below). In the CVD process, carbonsources in the gas phase flowing through a heating furnace decompose anddissolve on the surface of active catalyst nanoparticles, initiating the growthof CNTs. Since the successful CVD growth of SWCNTs in the late 1990s, ahuge amount of work has been reported on growing CNTs by this technique[74–78]. It has been revealed that various CNTs with different morphologies andcrystallinity can be generated by adjusting the parameters including the carbonfeedstock, catalyst (composition, size, shape, density, and crystal structure),carrier gas, temperature, and even the direction of gas flow and tube furnace.Furthermore, aligned CNTs (vertical or horizontal) with designed patterns canalso be obtained based on the CVD technique [79–81].

1.3.1.4Synthesis of CNTs with a Defined StructureNowadays, it has been realized that the crucial point for practical applicationsof CNTs is to obtain sufficient amount of a single type of CNTs with defineddiameter and chirality. Many research groups have contributed to this effortby optimizing the characteristics of the catalysts used in the CVD process. Forexample, Harutyunyan et al. increased the fraction of metallic SWCNTs up to91% by optimizing the thermal annealing conditions of the Fe nanocatalyst [82].Wang et al. reported their work on the growth a single type of SWCNTs (9, 8) with51.7% abundance by using a sulfate-promoted CoSO4/SiO2 catalyst [83]. Mostrecently, Li and colleagues successfully obtained specific SWCNTs (12, 6) with anabundance over 92% in their CVD growth studies [84]. W6Co7 alloy nanoclusterswith specific structural features were used as the catalyst and believed to be thekey factor to initialize the SWCNT’s specific growth. These works demonstratedthe possibility to directly grow structure-controlled CNTs, which is of greatimportance to achieve CNT applications for nanoelectronics and biologicalpurposes.


1.3.2Functionalization

Before applying CNTs to a certain applications, it is usually required to modifythe surface of CNTs for functionalization, better dispersion, and feasible manip-ulation. There have been a large number of reports on the surface modificationsof CNTs, which can be generally classified as covalent chemistry and noncovalentmodifications.

1.3.2.1Covalent Chemical ReactionsThere are usually some impurities (amorphous carbon, catalyst particles, etc.) inthe raw soot of CNTs. During the purification processes using acid oxidation,oxygenated functional groups are induced onto CNTs, mainly carbonyl and car-boxylic groups. The most widely used covalent chemical reactions of CNTs arethrough amidation based on the carboxylic groups on the surface or the openends of the nanotubes. Many other chemical reactions, such as Prato reaction,halogenation, cycloaddition, necleophilic addition, and radical addition, amongothers, have also been reported. The related reaction route, mechanism, and char-acterizations have been reported in several reviews [85, 86].

1.3.2.2Noncovalent ModificationsWrapping the CNTs with surfactants, biomolecules, and various types of poly-mers is another effective way to disperse and functionalize CNTs. This approachtakes advantage of the nonspecific interactions (mainly hydrophobic affinity andπ–π stacking) between the graphite surface of CNTs and hydrophobic moietiesor aromatic rings of the reactants. A wide variety of surfactants (ionic and non-ionic) have been used to wrap and disperse CNTs, such as sodium dodecyl sulfate,sodium cholate, sodium pyrenebutyrate, Tween, Triton, and so on. It has beenfound that bile salts are exceptionally effective for dispersing CNTs due to theirunique structure comprising a steroid ring and facial amphiphiles [87, 88]. Thesetypes of surfactants were utilized to obtain stable, monodispersed SWCNTs suit-able for diameter sorting using density gradient ultracentrifugation.

Modification Using Biomolecules Different types of biomolecules are used for thedispersion and functionalization of CNTs. Among them, DNA molecules haveproven to be highly effective through helical wrapping onto the CNT surface [89].On the basis of their outstanding dispersion efficiency, DNA sequences were ableto further recognize and separate structure-specific CNTs [90]. Moreover, phos-phate lipid-functionalized short CNTs can self-insert into lipid bilayers and livecell membranes to form biomimetic ion channels able to transport water, pro-tons, small ions, and DNA [91]. Some proteins, such as bovine serum albumin andstreptavidin, were also widely used for surface modification and possible furtherfunctionalization of CNTs, especially for biological applications.


Modification Using PEG-based Polymers The integration between CNTs andpolymers has been extensively investigated. To fabricate high-performanceCNT–polymer composites, CNTs were dispersed and bonded with variousspecies of polymers, such as poly(acrylate), hydrocarbon polymers, and conju-gated polymers, to name a few [85]. Meanwhile, for biological purposes, blockcopolymers comprising hydrophobic chains and hydrophilic poly(ethylene glycol)(PEG) are the most widely used reagents to modify and disperse CNTs in highlysalted aqueous solutions and biofluids [92]. It is well known that the PEG moietiesover the CNT surface can prevent nonspecific protein adsorption and increasethe biocompatibility of CNTs. PEG chains with different lengths and branchstructures have been attached to CNTs. Among them, phosphate–lipid conju-gated PEG polymers were the most commonly used to form stable suspension ofCNTs in solutions with high ionic strength [93]. A comb-shaped PEG branch wasproven to have higher dispersion efficiency as a result of the higher density of PEGchains above the hydrophobic graphite surface [94]. It was also possible to furtherenhance the dispersion ability of PEG polymers by adjusting the linker structurebetween the hydrophobic and the PEG chains. For example, it was found thatceramide-conjugated PEG, which has a neutral linker group, possesses a higherdispersion potential than the corresponding charged phospholipid-conjugatedPEG polymers [95].

1.3.3Characterization

Different from real molecules, a CNT sample is actually a mixture containingCNTs with different diameters, lengths, and chirality. They cannot form realsolutions or identical crystals. Therefore, many analysis methods commonly usedin molecular chemistry, such as X-ray diffraction crystallography, NMR, and soon, are not effective for identifying the exact chemical composition and bindinginformation of CNTs and the attached functional groups. Alternative methods areadopted to obtain the structural features of CNTs and functionalized derivativesto some extent, which include transmission electron microscopy (TEM), atomicforce microscopy (AFM), Raman spectroscopy, ultraviolet–visible (UV–vis)absorbance spectroscopy, and near-infrared (NIR) fluorescence.

1.3.3.1Microscopic CharacterizationsAmong these analysis tools, TEM is a widely used method to characterize CNTswith respect to their morphology and composition information. It is also a pow-erful tool to study in situ dynamic processes in the nanoscale. For example, Sue-naga et al. [96] were able to directly image Stone–Wales defects in SWCNTs andtheir propagation under heating by means of high-resolution TEM with atomicresolution. The development of this technique in recent years has made it pos-sible to achieve elemental analysis using electron energy loss spectroscopy to an


unprecedented sensitivity, even at the atomic level [97]. Compared to TEM, AFMis more versatile and nondestructive. The morphology and conformation of theattached soft materials on the surface of CNTs, such as DNA and proteins, wereable to be analyzed by AFM observations [98]. Moreover, tip-enhanced Ramanspectroscopy integrated with AFM is regarded as a fantastic tool for chemicalanalysis at the nano-scale [99]. It holds promise to detect single molecules on sur-faces, although the current sensitivity is still limited by the use of conventionalAFM tips. The newly developed multiple-probe AFM is a specialized method thatallows researchers to manipulate up to four AFM probes at the same time [100]. Itaffords flexible and precise control of the tip location and tip–sample force whenthe tips are used as electrodes for probing the electrical properties of individ-ual CNTs.

1.3.3.2Spectroscopic CharacterizationsSpectroscopic methods are also very useful in obtaining structural informationof CNTs, which is especially important to identify the functionalized chemicalspecies on CNTs. Raman spectroscopy is a versatile and sensitive tool that hasbeen utilized from the very beginning of CNT studies [101, 102]. It is possible toidentify a single CNT based on its resonance Raman spectrum, giving structuralcharacteristics including the diameter, defect density, surface functionality, andmuch beyond. It has been a standard tool in the studies of nanocarbon materials.UV–vis absorbance and NIR fluorescence are commonly used to analyze CNTsamples dispersed in solution [103]. Both methods are very sensitive to the disper-sion state of functionalized CNTs in solution (individuals or bundles). Especially,UV–vis measurements are very easy to perform, and can give valuable informa-tion of CNTs on the dispersion state, preliminary chemical functional compo-nents, diameter, chirality, and even the length.

1.3.4Questions and Future Directions

Based on their outstanding structural features and properties, CNTs are expectedto be used in various applications, including electronic devices, sensors, andbiological uses. However, to effect these practical applications, it is necessaryto obtain the CNT samples having a defined structure. The diameter, chirality,and even the length of a CNT affect its electrical and biological properties. Asmentioned above, researchers have been able to synthesize CNT samples withidentical chirality. It is also possible to separate CNTs having a certain structuralfeature by density-gradient ultracentrifugation. But, until now, the amount of thepure CNTs produced is too small to be applied to practical applications. It is ofcritical importance to produce pure CNTs of a defined structure in a reproducibleand economical way to achieve practical applications of this amazing materialafter over two decades of its discovery.


1.4Graphene

Graphene, a single sp2-bonding carbon layer of the graphite structure, is abasic building block for graphitic materials of all other dimensionalities. Itcan be wrapped up into 0D fullerenes, rolled into 1D nanotubes, and stackedinto 3D graphite (Figure 1.4a) [104]. It has potential to exhibit a wide range ofremarkable structural and transport properties, for example, specific surfacearea, high carrier mobility (>200 000 cm2 V−1 s−1) [108, 109], high Young’s mod-ulus (∼1100 GPa) [110], excellent optical transparency [111], and high thermalconductivity (∼5000 W m−1 K−1) [112]. These peculiar properties arise from itsunique electronic band structure, in which the conduction band overlaps with thevalence band at two points (K and K′) in the Brillouin zone, and in the vicinity ofthese points the electron energy exhibits a linear relationship with the wave vector(Figure 1.4b) [105]. The experimental observations of the extraordinary transportproperties have fueled extensive research on its chemical and physical properties[113, 114]. Although the experimentally observed values are substantially lowerthan theoretical predictions, research into graphene to date has highlighted thepotential for applications in nanodevices, energy-storage materials, polymercomposites, liquid crystal devices, and biomedicine [115, 116]. In this section, weaim to summarize the progress made on graphene, ranging from the synthesis andcharacterization to functionalization. Clearly, the development of various meth-ods for producing graphene with controllable quality, quantity, and morphologymight enable us to expand the graphene family with fascinating properties.

1.4.1Synthesis and Characterization

In extensive studies to date, four different routes have been reported to producegraphene. The first was the micromechanical exfoliation of graphite, named asthe “Scotch tape” or peel-off method [113]. This approach was inspired by earlierwork on the micromechanical exfoliation from patterned graphite [117]. The sec-ond was CVD, such as the decomposition of a carbon source on metal substrates,for example, copper and nickel [118, 119]. The third was the epitaxial growth onelectrically insulating surfaces, for example, SiC [120]. The fourth was the liquid-phase exfoliation of graphite into graphene nano-platelets [121].

The resulting graphene obtained by the above methods exhibit diversitiesin sample size and quality, implying their applicability for niche applications.Micromechanical exfoliation has, for example, yielded the highest quality butwith small sample sizes ranging from few micrometers to ∼1 mm, which areapplicable only for fundamental studies on their transport properties. Large-area,uniform, and continuous graphene films are now achievable by CVD on Cu foil,but they exhibit moderate charge carrier mobility. A complete process requiresthe transfer from the Cu foil to a target substrate, and the production of squaremeters of graphene has already been achieved. The polymers used as a supporting

1.4 Graphene 15

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layer in the transferring procedure, however, are rather difficult to be completelyremoved from the graphene surface. The residual polymers are found to greatlyinfluence the graphene’s properties and thus make the materials properties lesscontrollable in devices. CVD-grown graphene films are ready for use in transpar-ent conductive coating applications, sensors, and nanoelectronics, although thereare defects, grain boundaries, and thicker graphene that would result in variabledevice performance from one device to another. The quality of graphene grownon SiC can be very high, with crystallites approaching hundreds of micrometersin size. Thus, SiC-grown graphene may find application in high-frequencytransistors. In the liquid exfoliation of graphite, intercalation of solvents into thegallery of graphite favors the interlayer expansion. With further aids of sonicationand thermal or plasma processes, such graphite intercalated compounds can sub-sequently be delaminated into graphene nano-platelets, with a wide dispersion ofthickness and lateral size, strongly depending on the treatment conditions [121].The tone-scale synthesis of graphene via this method is currently being evaluatedin numerous applications in printed electronics, electromagnetic shielding,barrier coatings, heat dissipation, supercapacitors, and so on [122].

The peculiar chemical and physical properties of graphene have demonstratedexperimentally a strong dependence on the number of graphene layers, thequality of the material, the type of defects, and the substrates. In this context, it isof critical importance to perform various characterizations on graphene in orderto explore the issues mentioned above. Optical microscopy is a quick and precisemethod to rapidly locate graphene and to determine the thickness of graphenenano-platelets in terms of their contrast spectrum. One can observe a contrastbetween the graphene layers and SiO2(285 nm)/Si substrate in a reflectionspectrum using a normal white-light illumination on samples supported on asubstrate (Figure 1.4c) [106]. The graphene sample shows four different contrastregions, which are related to four different thicknesses. By fitting the experimentaldata to Fresnel’s law, the experimental refractive index of a single-layer graphenen= 2.0− 1.1i differs from that of bulk graphite n= 2.6− 1.3i in the visible range.Such a large deviation was ascribed to the decrease of interlayer interaction inthe ultrathin range. In similar cases, the thickness of few-layer graphene withless than 10 layers has clearly been discriminated. As to a continuous graphenefilm on a Cu foil by CVD, scanning electron microscopy (SEM) is an efficientmethod for the direct evaluation. Figure 1.4d depicts a higher resolution image ofgraphene on Cu with the presence of Cu surface steps, graphene “wrinkles,” andthe presence of nonuniform dark flakes. The wrinkles are caused by the thermalexpansion coefficient difference between Cu and graphene. The CVD-growngraphene also exhibits a clear contrast between the graphene layers when it istransferred onto the SiO2(285 nm)/Si substrate (Figure 1.4e).

Raman spectroscopy is another nondestructive and quick inspection methodfor evaluating the thickness and quality of graphene. In the Raman spectra ofgraphene, a G peak located at ∼1580 cm−1 and a 2D peak at ∼2700 cm−1 areobserved, as shown in Figure 1.4f, corresponding to the in-plane optical vibration(degenerate zone-center E2g mode) and second-order of zone-boundary phonons,

1.4 Graphene 17

respectively [107]. The D peak, located at ∼1350 cm−1 due to first-order zoneboundary phonons, is absent from defect-free graphene. It will be activated bydefects, vacancy, and structural disorder in graphene. The number of layers ingraphene can be determined by the shape, width, and position of the 2D peak.Figure 1.4g and h shows that the 2D peak shifts to higher wavenumber valuesand becomes broader with an increase in the number of layers. For more thanfive layers, however, the Raman spectrum becomes hardly distinguishable fromthat of bulk graphite. Raman spectroscopy has also been useful in identifyingthe quality and types of edge, the effects of perturbations, such as electric andmagnetic fields, strain, doping, disorder, and functional groups [123].

1.4.2Functionalization of Graphene and Graphene Oxide

The chemical modification of graphene generally includes covalent attachment oforganic molecules, hydrogen, and halogens to pristine graphene and/or its deriva-tives, noncovalent functionalization, and deposition of various nanoparticles onit [124].

Graphene and graphene oxide with large surface area, delocalized π electrons,and easy functionalization by various molecules provide opportunities forapplications in nanodevices, energy-storage materials, and polymer composites[115]. In terms of the solid-state 13C NMR spectroscopy analysis done to date(Figure 1.2a–c) [125, 126], the possible structural model of graphene oxide hasbeen proposed in Figure 1.4d [126]. The carbon network is bonded to hydroxylgroups or epoxide groups as well as five- and six-membered lactols. Most ofcovalent functionalization methods rely on these groups that are active sites.

Covalent chemistry has proven to be an effective path to convert the sp2-hybridized carbon atoms into sp3-hybridized ones by forming a single bond withexternal groups. For example, the aryl radicals dissociated from diazonium saltsupon heating broke the –C==C– double bonds and introduced aryl groups ontothe graphene plane [127]. By use of photoinduced free radicals, one can alsointroduce aryl groups onto graphene scaffold from benzoyl peroxide. However,the free-radical reactions usually give rise to disordered crystal structures [128].

It would be ideal to control the crystal structure and chemical compositionof graphene derivatives. Theoretical calculations predicted the existence of fullyhydrogenated and fluorinated graphene from both sides, named as graphane andfluorographene, respectively [129–131]. Graphane and fluorographene are boththermodynamically stable with a C/H or C/F ratio of 1:1. Graphane has two stableconfigurations: a chair conformer and a boat conformer, the former being slightlymore stable than the latter. The direct bandgap values at the K point are 3.5 and3.7 eV for the former and latter, respectively. By exposing free-standing grapheneto a hydrogen plasma, one can achieve the double-sided hydrogenation ofgraphene [132]. The electron diffraction (ED) pattern revealed that the graphanehas a hexagonal symmetry with a lattice constant d = 2.46± 0.02 Å, which is ∼1%smaller than that of pristine graphene. This lattice shrinkage after exposure to H


radicals arises from the change of carbon configuration from sp2 to sp3, whichgenerally results in longer C–C bonds. The unit cell of fluorographene is, incontrast, ∼1% larger than that of graphene as a consequence of the corrugation[133], whereas the measured unit cell of C2F chair, partially fluorinated grapheneon one side, revealed a 2.4% expansion with respect to graphene, which islarger than corrugated fluorographene. The C2F chair, one-sided fluorination ofgraphene, demonstrated a much higher degree of pristine long-range structuraland morphological order than fluorographene [134]. The tetragonal “boat” formexhibits a short-range order.

Noncovalent functionalization involves the reactions with biocompatiblepolymers or biomolecules via hydrophobic interactions, π–π stacking, or electro-static interactions. Such modification greatly improves their stability in aqueoussolutions. Since graphene oxide nanosheets are negatively charged, a positivelycharged polyelectrolyte (PEI) can effectively bind with them via electrostaticinteractions. The resulting nano-graphene oxide (nGO)/PEI hybrids, for example,show much improved physiological stability compared to graphene oxide, reducedtoxicity compared to bare PEI, and high gene transfection efficiency [135].

Deposition of nanoparticles, including those of metals (e.g., Au, Ag, Pd, Pt, Ni,and Cu) and metal oxides (TiO2, ZnO, MnO2, Co3O4, and Fe3O4), on grapheneand nGO demonstrates the potential for their applications in biomedicine [136].For example, graphene oxide/iron oxide nanoparticle composites have beeninvestigated for magnetic targeted drug delivery and in vivo multimodal-imaging-guided photothermal therapy because of their interesting magnetic and opticalproperties.

Biofunctionalization of graphene and graphene oxide with biomoleculesand cells have expanded their applications to a variety of biological platforms,biosensors, and biodevices. Until now, a number of biomolecules, for example,nucleic acids (NAs), peptides, proteins and cells, have been successfully employedin biological modification of graphene and graphene oxide (Figure 1.5a) [137].One can also achieve its surface modification through reaction with varioushydrophilic macromolecules, such as PEG (Figure 1.5b–f) [138], amine-modifieddextran (DEX) [139], and poly(acrylic acid) (PAA) [140]. The modified grapheneoxides have exhibited improved biocompatibility, reduced nonspecific binding tobiological molecules and cells, and improved in vivo pharmacokinetics for bettertumor targeting [138].

1.4.3Prospects and Challenges

In more than 10 years of worldwide research, graphene and its derivatives withfascinating properties have shown potential for applications. Toward theseapplications, mass production techniques are required to produce uniformgraphene nano-platelets. Low-temperature growth of large-area, uniform,high-quality bilayer and multilayer graphene films on arbitrary substrates needto be developed. The efficient, intact, and clean transfer from metal substrates

1.4 Graphene 19

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of graphene oxide: photos of (c) GO and(d) nGO–PEG in different solutions recordedafter centrifugation at 10 000g for 5min.GO crashed out slightly in PBS and com-pletely in cell medium and serum (toppanel). nGO–PEG was stable in all solutions.AFM images of (e) GO and (f ) nGO–PEG.(Reprinted with permission from [138]. ©2008American Society Chemistry.)


without etching the metals remains challenging. The combination of grapheneand biotechnology is still in its infancy. There are many issues to be resolvedbefore putting graphene to bioapplications. The potential long-term toxicityhas been central to these issues. Whether and how graphene and its derivativesgradually degrade in biological system is essentially unclear. Its influence on theimmune and reproductive systems of animals requires more research activities.

1.5Summary and Outlook

In the past three decades, researchers all over the world have carried out extensivestudies on carbon nanomaterials, especially fullerenes, CNTs, and graphene. Var-ious methods to synthesize these nanomaterials with different morphology andstructures have been reported. Diverse and attractive mechanical, chemical, andphysical properties have also been investigated by means of state-of-the-art char-acterization tools. Based on these comprehensive studies, carbon nanomaterialsare believed to have the potential for use in many exciting applications in manyfields.

However, most of the proposed applications have not been realized. Till now, itis widely accepted that the biggest challenge to achieve these practical applicationsis obtaining enough amount of carbon nanomaterials having a designated struc-ture. Researchers are now reconsidering ways to synthesize carbon nanomaterials.

The first thing is to set up effective methods to produce carbon nanomaterialswith a precisely controlled structure and identical properties. The chirality,diameter, layer number, and even the assembly status of CNTs may changetheir optical, electrical, and biological behaviors dramatically. Similarly, the layernumber, width, edge structure, and defect number of graphene determine itsproperties and feasible applications. Therefore, a uniform sample having the samestructure is required for many real applications, especially in the electrical andbiological fields.

The second consideration is the production yield. Now it is possible to syn-thesize or separate identical fullerene isomers and CNTs of a single chirality.Graphene ribbons in a narrow range of widths were also successfully engineeredin the laboratory. The problem is that the obtained amount is far below that isneeded for practical usage. It remains a big challenge to improve the yield of thesematerials with structural purity. On the other hand, researchers are currentlyable to produce CNTs and graphene on an industrial scale despite the precisecontrol on their fine structures, which greatly promote the progress toward someapplications such as films, composites, and surface coating. In this aspect, it willbe very helpful to further decrease the production cost and keep a comparativelyhigh structural quality at the same time.

In conclusion, to achieve practical applications, the primary goal and task is toscale up the production of carbon nanomaterials in a reproducible way, preferablywith a precise control on their fine structures.

References 21

References

1. Heath, J.R., Zhang, Q., O’Brien, S.C.,Curl, R.F., Kroto, H.W., and Smalley,R.E. (1987) The formation of longcarbon chain molecules during laservaporization of graphite. J. Am. Chem.Soc., 109, 359–363.

2. Heath, J.R., O’Brien, S.C., Zhang, Q.,Liu, Y., Curl, R.F., Tittel, F.K., andSmalley, R.E. (1985) Lanthanum com-plexes of spheroidal carbon shells.J. Am. Chem. Soc., 107, 7779–7780.

3. Chai, Y., Guo, T., Jin, C., Haufler, R.E.,Chibante, L.P.F., Fure, J., Wang, L.,Alford, J.M., and Smalley, R.E. (1991)Fullerenes with metals inside. J. Phys.Chem., 95, 7564–7568.

4. Stevenson, S., Rice, G., Glass, T.,Harich, K., Cromer, F., Jordan, M.R.,Craft, J., Hadju, E., Bible, R., Olmstead,M.M., Maitra, K., Fisher, A.J., Balch,A.L., and Dorn, H.C. (1999) Small-bandgap endohedral metallofullerenesin high yield and purity. Nature, 401,55–57.

5. Yang, S., Zhang, L., Zhang, W., andDunsch, L. (2010) A facile route tometal nitride clusterfullerenes by usingguanidinium salts: a selective organicsolid as the nitrogen source. Chem. Eur.J., 16, 12398–12405.

6. Mercado, B.Q., Olmstead, M.M.,Beavers, C.M., Easterling, M.L.,Stevenson, S., Mackey, M.A., Coumbe,C.E., Phillips, J.D., Phillips, J.P., Poblet,J.M., and Balch, A.L. (2010) A sevenatom cluster in a carbon cage, the crys-tallographically determined structure ofSc4([small mu ]3-O)3@Ih-C80. Chem.Commun., 46, 279–281.

7. Chen, N., Chaur, M.N., Moore,C., Pinzon, J.R., Valencia, R.,Rodriguez-Fortea, A., Poblet, J.M.,and Echegoyen, L. (2010) Synthesisof a new endohedral fullerene family,Sc2S@C2n (n = 40-50) by the intro-duction of SO2. Chem. Commun., 46,4818–4820.

8. Lu, X., Shi, Z.J., Sun, B.Y., He, X.R.,and Gu, Z.N. (2005) Isolation andspectroscopic study of a series of

monogadolinium endohedral metallo-fullerenes. Fullerenes Nanotubes CarbonNanostruct., 13, 13–20.

9. Feng, L., Sun, B.Y., He, X.R., and Gu,Z.N. (2002) Isolation and spectroscopicstudy of a series of monoterbium endo-hedral metallofullerenes. FullerenesNanotubes Carbon Nanostruct., 10,353–361.

10. Akasaka, T., Okubo, S., Kondo, M.,Maeda, Y., Wakahara, T., Kato, T.,Suzuki, T., Yamamoto, K., Kobayashi,K., and Nagase, S. (2000) Isolation andcharacterization of two Pr@C82 iso-mers. Chem. Phys. Lett., 319, 153–156.

11. Diener, M.D. and Alford, J.M. (1998)Isolation and properties of small-bandgap fullerenes. Nature, 393,668–671.

12. Wakahara, T., Nikawa, H., Kikuchi,T., Nakahodo, T., Rahman, G.M.A.,Tsuchiya, T., Maeda, Y., Akasaka, T.,Yoza, K., Horn, E., Yamamoto, K.,Mizorogi, N., Slanina, Z., and Nagase,S. (2006) La@C72 having a non-IPRcarbon cage. J. Am. Chem. Soc., 128,14228–14229.

13. Nikawa, H., Kikuchi, T., Wakahara, T.,Nakahodo, T., Tsuchiya, T., Rahman,G.M.A., Akasaka, T., Maeda, Y., Yoza,K., Horn, E., Yamamoto, K., Mizorogi,N., and Nagase, S. (2005) Missing met-allofullerene La@C74. J. Am. Chem.Soc., 127, 9684–9685.

14. Nikawa, H., Yamada, T., Cao, B.P.,Mizorogi, N., Slanina, Z., Tsuchiya,T., Akasaka, T., Yoza, K., and Nagase,S. (2009) Missing metallofullerenewith C80 cage. J. Am. Chem. Soc., 131,10950–10954.

15. Akasaka, T., Lu, X., Kuga, H., Nikawa,H., Mizorogi, N., Slanina, Z., Tsuchiya,T., Yoza, K., and Nagase, S. (2010)Dichlorophenyl derivatives ofLa@C3v(7)-C82: endohedral metalinduced localization of pyramidalizationand spin on a triple-hexagon junction.Angew. Chem. Int. Ed., 49, 9715–9719.

16. Chaur, M.N., Melin, F., Ashby, J.,Elliott, B., Kumbhar, A., Rao, A.M.,and Echegoyen, L. (2008) Lan-thanum nitride endohedral fullerenes


La3N@C2n (43 <= n <= 55): preferen-tial formation of La3N@C96. Chem. Eur.J., 14, 8213–8219.

17. Shinohara, H., Yamaguchi, H., Hayashi,N., Sato, H., Ohkohchi, M., Ando,Y., and Saito, Y. (1993) Isolation andspectroscopic properties of scan-dium fullerenes (Sc2@C74, Sc2@C82,and Sc2@C84). J. Phys. Chem., 97,4259–4261.

18. Klute, R.C., Dorn, H.C., and McNair,H.M. (1992) HPLC separation of higher(C84+) fullerenes. J. Chromatogr. Sci.,30, 438–442.

19. Meier, M.S. and Selegue, J.P. (1992)Efficient preparative separation of C60and C70. Gel permeation chromatog-raphy of fullerenes using 100% tolueneas mobile phase. J. Org. Chem., 57,1924–1926.

20. Bolskar, R.D. and Alford, J.M. (2003)Chemical oxidation of endohedralmetallofullerenes: identification andseparation of distinct classes. Chem.Commun., 1292–1293.

21. Stevenson, S., Harich, K., Yu, H.,Stephen, R.R., Heaps, D., Coumbe,C., and Phillips, J.P. (2006) Nonchro-matographic “Stir and Filter Approach”(SAFA) for isolating Sc3N@C80 met-allofullerenes. J. Am. Chem. Soc., 128,8829–8835.

22. Stevenson, S., Mackey, M.A., Coumbe,C.E., Phillips, J.P., Elliott, B., andEchegoyen, L. (2007) Rapid removalof D5h isomer using the “stir and filterapproach” and isolation of large quan-tities of isomerically pure Sc3N@C80metallic nitride fullerenes. J. Am. Chem.Soc., 129, 6072–6073.

23. Lu, X., Feng, L., Akasaka, T., andNagase, S. (2012) Current status andfuture developments of endohedralmetallofullerenes. Chem. Soc. Rev., 41,7723–7760.

24. Yamada, M., Someya, C., Wakahara,T., Tsuchiya, T., Maeda, Y., Akasaka,T., Yoza, K., Horn, E., Liu, M.T.H.,Mizorogi, O.N., and Nagase, S.(2008) Metal atoms collinear withthe spiro carbon of 6,6-open adducts,M2@C80(Ad) (M = La and Ce, Ad =adamantylidene). J. Am. Chem. Soc.,130, 1171–1176.

25. Xie, Y., Suzuki, M., Cai, W., Mizorogi,N., Nagase, S., Akasaka, T., and Lu, X.(2013) Highly regioselective addition ofadamantylidene carbene to Yb@C2v(3)-C80 to afford the first derivative ofdivalent metallofullerenes. Angew.Chem. Int. Ed., 52, 5142–5145.

26. Zhang, W., Suzuki, M., Xie, Y., Bao,L., Cai, W., Slanina, Z., Nagase, S.,Xu, M., Akasaka, T., and Lu, X. (2013)Molecular structure and chemicalproperty of a divalent metallofullereneYb@C2(13)-C84. J. Am. Chem. Soc.,135, 12730–12735.

27. Feng, L., Wakahara, T., Nakahodo,T., Tsuchiya, T., Piao, Q., Maeda, Y.,Lian, Y., Akasaka, T., Horn, E., Yoza,K., Kato, T., Mizorogi, N., and Nagase,S. (2006) The Bingel monoadducts ofLa@C82: synthesis, characterization,and electrochemistry. Chem. Eur. J., 12,5578–5586.

28. Yamada, M., Wakahara, T., Nakahodo,T., Tsuchiya, T., Maeda, Y., Akasaka,T., Yoza, K., Horn, E., Mizorogi, N.,and Nagase, S. (2006) Synthesis andstructural characterization of endo-hedral pyrrolidinodimetallofullerene:La2@C80(CH2)2NTrt. J. Am. Chem.Soc., 128, 1402–1403.

29. Akasaka, T., Kato, T., Kobayashi, K.,Nagase, S., Yamamoto, K., Funasaka,H., and Takahashi, T. (1995) Exohe-dral adducts of La@C82. Nature, 374,600–601.

30. Popov, A.A., Yang, S., and Dunsch, L.(2013) Endohedral fullerenes. Chem.Rev., 113, 5989–6113.

31. Maeda, Y., Sato, S., Inada, K., Nikawa,H., Yamada, M., Mizorogi, N.,Hasegawa, T., Tsuchiya, T., Akasaka,T., Kato, T., Slanina, Z., and Nagase,S. (2010) Regioselective exohedralfunctionalization of La@C82 and its1,2,3,4,5-pentamethylcyclopentadieneand adamantylidene adducts. Chem.Eur. J., 16, 2193–2197.

32. Lu, X., Nikawa, H., Tsuchiya, T.,Akasaka, T., Toki, M., Sawa, H.,Mizorogi, N., and Nagase, S. (2010)Nitrated benzyne derivatives ofLa@C82: addition of NO2 and its

References 23

positional directing effect on the sub-sequent addition of benzynes. Angew.Chem. Int. Ed., 49, 594–597.

33. Takano, Y., Yomogida, A., Nikawa, H.,Yamada, M., Wakahara, T., Tsuchiya,T., Ishitsuka, M.O., Maeda, Y., Akasaka,T., Kato, T., Slanina, Z., Mizorogi, N.,and Nagase, S. (2008) Radical couplingreaction of paramagnetic endohedralmetallofullerene La@C82. J. Am. Chem.Soc., 130, 16224–16230.

34. Shu, C., Slebodnick, C., Xu, L.,Champion, H., Fuhrer, T., Cai, T., Reid,J.E., Fu, W., Harich, K., Dorn, H.C., andGibson, H.W. (2008) Highly regioselec-tive derivatization of trimetallic nitridetemplated endohedral metallofullerenesvia a facile photochemical reaction.J. Am. Chem. Soc., 130, 17755–17760.

35. Fang, H., Cong, H., Suzuki, M., Bao, L.,Yu, B., Xie, Y., Mizorogi, N., Olmstead,M.M., Balch, A.L., Nagase, S., Akasaka,T., and Lu, X. (2014) Regioselectivebenzyl radical addition to an open-shellcluster metallofullerene. Crystal-lographic studies of cocrystallizedSc3C2@Ih-C80 and its singly bondedderivative. J. Am. Chem. Soc., 136,10534–10540.

36. Tsuchiya, T., Kurihara, H., Sato, K.,Wakahara, T., Akasaka, T., Shimizu,T., Kamigata, N., Mizorogi, N., andNagase, S. (2006) Supramolecular com-plexes of La@C82 with unsaturatedthiacrown ethers. Chem. Commun.,3585–3587.

37. Tsuchiya, T., Sato, K., Kurihara, H.,Wakahara, T., Maeda, Y., Akasaka, T.,Ohkubo, K., Fukuzumi, S., Kato, T., andNagase, S. (2006) Spin-site exchangesystem constructed from endohedralmetallofullerenes and organic donors.J. Am. Chem. Soc., 128, 14418–14419.

38. Takata, M., Umeda, B., Nishibori, E.,Sakata, M., Saito, Y., Ohno, M., andShinohara, H. (1995) Confirmation byX-ray diffraction of the endohedralnature of the metallofullerene [email protected], 377, 46–49.

39. Nishibori, E., Ishihara, M., Takata,M., Sakata, M., Ito, Y., Inoue, T.,and Shinohara, H. (2006) Bent(metal)2C2 clusters encapsulated in(Sc2C2)@C82(III) and (Y2C2)@C82(III)

metallofullerenes. Chem. Phys. Lett.,433, 120–124.

40. Nishibori, E., Takata, M., Sakata, M.,Inakuma, M., and Shinohara, H. (1998)Determination of the cage structureof Sc@C82 by synchrotron powderdiffraction. Chem. Phys. Lett., 298,79–84.

41. Nishibori, E., Takata, M., Sakata,M., Tanaka, H., Hasegawa, M., andShinohara, H. (2000) Giant motion ofLa atom inside C82 cage. Chem. Phys.Lett., 330, 497–502.

42. Nishibori, E., Terauchi, I., Sakata,M., Takata, M., Ito, Y., Sugai, T.,and Shinohara, H. (2006) High-resolution analysis of (Sc3C2)@C80metallofullerene by third generationsynchrotron radiation X-ray powderdiffraction. J. Phys. Chem. B, 110,19215–19219.

43. Sun, B.Y., Sugai, T., Nishibori, E.,Iwata, K., Sakata, M., Takata, M., andShinohara, H. (2005) An anomalousendohedral structure of Eu@C82 met-allofullerenes. Angew. Chem. Int. Ed.,44, 4568–4571.

44. Tsuchiya, T., Wakahara, T., Maeda, Y.,Akasaka, T., Waelchli, M., Kato, T.,Okubo, H., Mizorogi, N., Kobayashi,K., and Nagase, S. (2005) 2D NMRcharacterization of the La@C82 anion.Angew. Chem. Int. Ed., 44, 3282–3285.

45. Yamada, M., Wakahara, T., Lian, Y.F.,Tsuchiya, T., Akasaka, T., Waelchli,M., Mizorogi, N., Nagase, S., andKadish, K.M. (2006) Analysis oflanthanide-induced NMR shifts ofthe Ce@C82 anion. J. Am. Chem. Soc.,128, 1400–1401.

46. Kurihara, H., Lu, X., Iiduka, Y.,Mizorogi, N., Slanina, Z., Tsuchiya,T., Akasaka, T., and Nagase, S. (2011)Sc2C2@C80 rather than Sc2@C82:templated formation of unexpectedC2v(5)-C80 and temperature-dependentdynamic motion of internal Sc2C2 clus-ter. J. Am. Chem. Soc., 133, 2382–2385.

47. Lu, X., Nakajima, K., Iiduka, Y., Nikawa,H., Mizorogi, N., Slanina, Z., Tsuchiya,T., Nagase, S., and Akasaka, T. (2011)Structural elucidation and regioselectivefunctionalization of an unexploredcarbide cluster metallofullerene


Sc2C2@Cs(6)-C82. J. Am. Chem. Soc.,133, 19553–19558.

48. Lu, X., Nakajima, K., Iiduka, Y., Nikawa,H., Tsuchiya, T., Mizorogi, N., Slanina,Z., Nagase, S., and Akasaka, T. (2012)The long-believed Sc2@C2v(17)-C84 isactually Sc2C2@C2v(9)-C82: unambigu-ous structure assignment and chemicalfunctionalization. Angew. Chem. Int.Ed., 51, 5889–5892.

49. Iiduka, Y., Wakahara, T., Nakajima, K.,Tsuchiya, T., Nakahodo, T., Maeda, Y.,Akasaka, T., Mizorogi, N., and Nagase,S. (2006) 13C NMR spectroscopicstudy of scandium dimetallofullerene,Sc2@C84 vs. Sc2C2@C82. Chem.Commun. (Camb.), 2057–2059.

50. Akasaka, T., Nagase, S., Kobayashi, K.,Walchli, M., Yamamoto, K., Funasaka,H., Kako, M., Hoshino, T., and Erata,T. (1997) 13C and 139La NMR studiesof La2@C80: first evidence for circularmotion of metal atoms in endohedraldimetallofullerenes. Angew. Chem. Int.Ed. Engl., 36, 1643–1645.

51. Lu, X., Akasaka, T., and Nagase,S. (2013) Carbide cluster metallo-fullerenes: structure, properties, andpossible origin. Acc. Chem. Res., 46,1627–1635.

52. Xu, W., Feng, L., Calvaresi, M., Liu, J.,Liu, Y., Niu, B., Shi, Z., Lian, Y., andZerbetto, F. (2013) An experimentallyobserved trimetallofullerene Sm-3@I-h-C-80: encapsulation of three metalatoms in a cage without a nonmetal-lic mediator. J. Am. Chem. Soc., 135,4187–4190.

53. Kobayashi, K. and Nagase, S. (2002)A stable unconventional structure ofSc2@C66 found by density functionalcalculations. Chem. Phys. Lett., 362,373–379.

54. Lee, H.M., Olmstead, M.M., Suetsuna,T., Shimotani, H., Dragoe, N.,Cross, R.J., Kitazawa, K., andBalch, A.L. (2002) Crystallographiccharacterization of Kr@C60 in(0.09Kr@C60/0.91C60)⋅{NiII(OEP)}⋅2C6H6. Chem. Commun., 1352–1353.

55. Che, Y., Yang, H., Wang, Z., Jin, H., Liu,Z., Lu, C., Zuo, T., Dorn, H.C., Beavers,C.M., Olmstead, M.M., and Balch,A.L. (2009) Isolation and structural

characterization of two very large, andlargely empty, endohedral fullerenes:Tm@C(3v)-C(94) and Ca@C(3v)-C(94).Inorg. Chem., 48, 6004–6010.

56. Yang, H., Jin, H., Zhen, H., Wang, Z.,Liu, Z., Beavers, C.M., Mercado, B.Q.,Olmstead, M.M., and Balch, A.L. (2011)Isolation and crystallographic identi-fication of four isomers of [email protected]. Am. Chem. Soc., 133, 6299–6306.

57. Aoyagi, S., Nishibori, E., Sawa, H.,Sugimoto, K., Takata, M., Miyata, Y.,Kitaura, R., Shinohara, H., Okada, H.,Sakai, T., Ono, Y., Kawachi, K., Yokoo,K., Ono, S., Omote, K., Kasama, Y.,Ishikawa, S., Komuro, T., and Tobita, H.(2010) A layered ionic crystal of polarLi@C60 superatoms. Nat. Chem., 2,678–683.

58. Hernandez-Eguia, L.P., Escudero-Adan,E.C., Pinzon, J.R., Echegoyen, L., andBallester, P. (2011) Complexation ofSc3N@C80 endohedral fullerene withcyclic Zn-bisporphyrins: solid stateand solution studies. J. Org. Chem., 76,3258–3265.

59. Dresselhaus, M.S., Dresselhaus, G., andJorio, A. (2004) Unusual properties andstructure of carbon nanotubes. Annu.Rev. Mater. Res., 34, 247–278.

60. Iijima, S. (1991) Helical microtubules ofgraphitic carbon. Nature, 354, 56–58.

61. Iijima, S. and Ichihashi, T. (1993)Single-shell carbon nanotubes of 1-nmdiameter. Nature, 363, 603–605.

62. Byrne, M.T. and Gun’ko, Y.K. (2010)Recent advances in research on carbonnanotube-polymer composites. Adv.Mater., 22, 1672–1688.

63. Spitalsky, Z., Tasis, D., Papagelis,K., and Galiotis, C. (2010) Carbonnanotube-polymer composites: chem-istry, processing, mechanical andelectrical properties. Prog. Polym. Sci.,35, 357–401.

64. McCarthy, M.A., Liu, B., Donoghue,E.P., Kravchenko, I., Kim, D.Y., So, F.,and Rinzler, A.G. (2011) Low-voltage,low-power, organic light-emittingtransistors for active matrix displays.Science, 332, 570–573.

65. Che, Y.C., Chen, H.T., Gui, H., Liu,J., Liu, B.L., and Zhou, C.W. (2014)

References 25

Review of carbon nanotube nano-electronics and macroelectronics.Semicond. Sci. Technol., 29, 073001.

66. Wilson, N.R. and Macpherson, J.V.(2009) Carbon nanotube tips for atomicforce microscopy. Nat. Nanotechnol., 4,483–491.

67. Wang, J., Hu, Z., Xu, J.X., and Zhao,Y.L. (2014) Therapeutic applicationsof low-toxicity spherical nanocarbonmaterials. NPG Asia Mater., 6, e84.

68. Bethune, D.S., Kiang, C.H., Devries,M.S., Gorman, G., Savoy, R., Vazquez,J., and Beyers, R. (1993) Cobalt-catalyzed growth of carbon nanotubeswith single-atomic-layerwalls. Nature,363, 605–607.

69. Journet, C., Maser, W.K., Bernier,P., Loiseau, A., de la Chapelle, M.L.,Lefrant, S., Deniard, P., Lee, R., andFischer, J.E. (1997) Large-scale produc-tion of single-walled carbon nanotubesby the electric-arc technique. Nature,388, 756–758.

70. Guo, T., Nikolaev, P., Rinzler, A.G.,Tomanek, D., Colbert, D.T., andSmalley, R.E. (1995) Self-assemblyof tubular fullerenes. J. Phys. Chem., 99,10694–10697.

71. Thess, A., Lee, R., Nikolaev, P., Dai,H.J., Petit, P., Robert, J., Xu, C.H., Lee,Y.H., Kim, S.G., Rinzler, A.G., Colbert,D.T., Scuseria, G.E., Tomanek, D.,Fischer, J.E., and Smalley, R.E. (1996)Crystalline ropes of metallic carbonnanotubes. Science, 273, 483–487.

72. Iijima, S., Yudasaka, M., Yamada, R.,Bandow, S., Suenaga, K., Kokai, F., andTakahashi, K. (1999) Nano-aggregatesof single-walled graphitic carbon nano-horns. Chem. Phys. Lett., 309, 165–170.

73. Azami, T., Kasuya, D., Yuge, R.,Yudasaka, M., Iijima, S., Yoshitake,T., and Kubo, Y. (2008) Large-scaleproduction of single-wall carbonnanohorns with high purity. J. Phys.Chem. C, 112, 1330–1334.

74. Dai, J.Y., Lauerhaas, J.M., Setlur, A.A.,and Chang, R.P.H. (1996) Synthesisof carbon-encapsulated nanowiresusing polycyclic aromatic hydrocarbonprecursors. Chem. Phys. Lett., 258,547–553.

75. Kong, J., Cassell, A.M., and Dai, H.J.(1998) Chemical vapor depositionof methane for single-walled carbonnanotubes. Chem. Phys. Lett., 292,567–574.

76. Li, Y., Liu, J., Wang, Y.Q., and Wang,Z.L. (2001) Preparation of monodis-persed Fe-Mo nanoparticles as thecatalyst for CVD synthesis of car-bon nanotubes. Chem. Mater., 13,1008–1014.

77. Zheng, B., Lu, C.G., Gu, G.,Makarovski, A., Finkelstein, G., andLiu, J. (2002) Efficient CVD growth ofsingle-walled carbon nanotubes on sur-faces using carbon monoxide precursor.Nano Lett., 2, 895–898.

78. Huang, S.M., Cai, X.Y., and Liu, J.(2003) Growth of millimeter-long andhorizontally aligned single-walled car-bon nanotubes on flat substrates. J. Am.Chem. Soc., 125, 5636–5637.

79. Hata, K., Futaba, D.N., Mizuno, K.,Namai, T., Yumura, M., and Iijima, S.(2004) Water-assisted highly efficientsynthesis of impurity-free single-waited carbon nanotubes. Science,306, 1362–1364.

80. Liu, Z.F., Jiao, L.Y., Yao, Y.G., Xian, X.J.,and Zhang, J. (2010) Aligned, ultralongsingle-walled carbon nanotubes: fromsynthesis, sorting, to electronic devices.Adv. Mater., 22, 2285–2310.

81. Jiang, K.L., Wang, J.P., Li, Q.Q., Liu,L.A., Liu, C.H., and Fan, S.S. (2011)Superaligned carbon nanotube arrays,films, and yarns: a road to applications.Adv. Mater., 23, 1154–1161.

82. Harutyunyan, A.R., Chen, G.G.,Paronyan, T.M., Pigos, E.M., Kuznetsov,O.A., Hewaparakrama, K., Kim,S.M., Zakharov, D., Stach, E.A., andSumanasekera, G.U. (2009) Preferen-tial growth of single-walled carbonnanotubes with metallic conductivity.Science, 326, 116–120.

83. Wang, H., Wei, L., Ren, F., Wang, Q.,Pfefferle, L.D., Haller, G.L., and Chen,Y. (2013) Chiral-selective CoSO4/SiO2catalyst for (9,8) single-walled car-bon nanotube growth. ACS Nano, 7,614–626.

84. Yang, F., Wang, X., Zhang, D.Q., Yang,J., Luo, D., Xu, Z.W., Wei, J.K., Wang,


J.Q., Xu, Z., Peng, F., Li, X.M., Li, R.M.,Li, Y.L., Li, M.H., Bai, X.D., Ding, F.,and Li, Y. (2014) Chirality-specificgrowth of single-walled carbon nan-otubes on solid alloy catalysts. Nature,510, 522524.

85. Tasis, D., Tagmatarchis, N., Bianco,A., and Prato, M. (2006) Chemistry ofcarbon nanotubes. Chem. Rev., 106,1105–1136.

86. Niyogi, S., Hamon, M.A., Hu, H., Zhao,B., Bhowmik, P., Sen, R., Itkis, M.E.,and Haddon, R.C. (2002) Chemistry ofsingle-walled carbon nanotubes. Acc.Chem. Res., 35, 1105–1113.

87. Wenseleers, W., Vlasov, I.I., Goovaerts,E., Obraztsova, E.D., Lobach, A.S., andBouwen, A. (2004) Efficient isolationand solubilization of pristine single-walled nanotubes in bile salt micelles.Adv. Funct. Mater., 14, 1105–1112.

88. Gubitosi, M., Trilo, J.V., Vargas, A.A.,Pavel, N.V., Gazzoli, D., Sennato, S.,Jover, A., Meijide, F., and Galantini,L. (2014) Characterization of carbonnanotube dispersions in solutions ofbile salts and derivatives containingaromatic substituents. J. Phys. Chem. B,118, 1012–1021.

89. Zheng, M., Jagota, A., Semke, E.D.,Diner, B.A., Mclean, R.S., Lustig, S.R.,Richardson, R.E., and Tassi, N.G. (2003)DNA-assisted dispersion and separationof carbon nanotubes. Nat. Mater., 2,338–342.

90. Tu, X.M., Manohar, S., Jagota, A.,and Zheng, M. (2009) DNA sequencemotifs for structure-specific recognitionand separation of carbon nanotubes.Nature, 460, 250–253.

91. Geng, J., Kim, K., Zhang, J.F., Escalada,A., Tunuguntla, R., Comolli, L.R.,Allen, F.I., Shnyrova, A.V., Cho, K.R.,Munoz, D., Wang, Y.M., Grigoropoulos,C.P., Ajo-Franklin, C.M., Frolov, V.A.,and Noy, A. (2014) Stochastic trans-port through carbon nanotubes inlipid bilayers and live cell membranes.Nature, 514, 612615.

92. Bottini, M., Rosato, N., and Bottini, N.(2011) PEG-modified carbon nanotubesin biomedicine: current status and chal-lenges ahead. Biomacromolecules, 12,3381–3393.

93. Liu, Z., Tabakman, S.M., Chen, Z.,and Dai, H.J. (2009) Preparation ofcarbon nanotube bioconjugates forbiomedical applications. Nat. Protoc., 4,1372–1382.

94. Matsumura, S., Sato, S., Yudasaka,M., Tomida, A., Tsruruo, T., Iijima,S., and Shiba, K. (2009) Preventionof carbon nanohorn agglomerationusing a conjugate composed of comb-shaped polyethylene glycol and apeptide aptamer. Mol. Pharmaceutics,6, 441–447.

95. Xu, J.X., Iijima, S., and Yudasaka, M.(2010) Appropriate PEG compoundsfor dispersion of single wall carbonnanohorns in salted aqueous solution.Appl. Phys. A, 99, 15–21.

96. Suenaga, K., Wakabayashi, H., Koshino,M., Sato, Y., Urita, K., and Iijima,S. (2007) Imaging active topologicaldefects in carbon nanotubes. Nat.Nanotechnol., 2, 358–360.

97. Suenaga, K. and Koshino, M.(2010) Atom-by-atom spectroscopyat graphene edge. Nature, 468,1088–1090.

98. Ge, C.C., Du, J.F., Zhao, L.N., Wang,L.M., Liu, Y., Li, D.H., Yang, Y.L., Zhou,R.H., Zhao, Y.L., Chai, Z.F., and Chen,C.Y. (2011) Binding of blood proteinsto carbon nanotubes reduces cytotoxi-city. Proc. Natl. Acad. Sci. U.S.A., 108,16968–16973.

99. Hartschuh, A. (2008) Tip-enhancednear-field optical microscopy. Angew.Chem. Int. Ed., 47, 8178–8191.

100. Nakayama, T., Kubo, O., Shingaya, Y.,Higuchi, S., Hasegawa, T., Jiang, C.S.,Okuda, T., Kuwahara, Y., Takami, K.,and Aono, M. (2012) Development andapplication of multiple-probe scanningprobe microscopes. Adv. Mater., 24,1675–1692.

101. Dresselhaus, M.S., Jorio, A., Hofmann,M., Dresselhaus, G., and Saito,R. (2010) Perspectives on carbonnanotubes and graphene Raman spec-troscopy. Nano Lett., 10, 751–758.

102. Dresselhaus, M.S., Jorio, A., and Saito,R. (2010) Characterizing graphene,graphite, and carbon nanotubes byRaman spectroscopy. Annu. Rev. Con-dens. Matter Phys., 1, 89–108.

References 27

103. Fagan, J.A., Bauer, B.J., Hobbie, E.K.,Becker, M.L., Walker, A.R.H., Simpson,J.R., Chun, J., Obrzut, J., Bajpai, V.,Phelan, F.R., Simien, D., Huh, J.Y., andMigler, K.B. (2011) Carbon nanotubes:measuring dispersion and length. Adv.Mater., 23, 338–348.

104. Geim, A.K. and Novoselov, K.S. (2007)The rise of graphene. Nat. Mater., 6,183–191.

105. Castro Neto, A.H., Guinea, F., Peres,N.M.R., Novoselov, K.S., and Geim,A.K. (2009) The electronic proper-ties of graphene. Rev. Mod. Phys., 81,109–162.

106. Ni, Z.H., Wang, H.M., Kasim, J., Fan,H.M., Yu, T., Wu, Y.H., Feng, Y.P., andShen, Z.X. (2007) Graphene thicknessdetermination using reflection andcontrast spectroscopy. Nano Lett., 7,2758–2763.

107. Ferrari, A.C., Meyer, J.C., Scardaci, V.,Casiraghi, C., Lazzeri, M., Mauri, F.,Piscanec, S., Jiang, D., Novoselov, K.S.,Roth, S., and Geim, A.K. (2006) Ramanspectrum of graphene and graphenelayers. Phys. Rev. Lett., 97, 187401.

108. Bolotin, K.I., Sikes, K.J., Jiang, Z.,Klima, M., Fudenberg, G., Hone, J.,Kim, P., and Stormer, H.L. (2008)Ultrahigh electron mobility in sus-pended graphene. Solid State Commun.,146, 351–355.

109. Morozov, S.V., Novoselov, K.S.,Katsnelson, M.I., Schedin, F., Elias,D.C., Jaszczak, J.A., and Geim, A.K.(2008) Giant intrinsic carrier mobilitiesin graphene and its bilayer. Phys. Rev.Lett., 100, 016602.

110. Lee, C., Wei, X.D., Kysar, J.W., andHone, J. (2008) Measurement of theelastic properties and intrinsic strengthof monolayer graphene. Science, 321,385–388.

111. Nair, R.R., Blake, P., Grigorenko, A.N.,Novoselov, K.S., Booth, T.J., Stauber, T.,Peres, N.M.R., and Geim, A.K. (2008)Fine structure constant defines visualtransparency of graphene. Science, 320,1308.

112. Balandin, A.A., Ghosh, S., Bao, W.Z.,Calizo, I., Teweldebrhan, D., Miao, F.,and Lau, C.N. (2008) Superior thermal

conductivity of single-layer graphene.Nano Lett., 8, 902–907.

113. Novoselov, K.S., Geim, A.K., Morozov,S.V., Jiang, D., Zhang, Y., Dubonos, S.V.,Grigorieva, I.V., and Firsov, A.A. (2004)Electric field effect in atomically thincarbon films. Science, 306, 666–669.

114. Zhang, Y.B., Tan, Y.W., Stormer, H.L.,and Kim, P. (2005) Experimental obser-vation of the quantum Hall effect andBerry’s phase in graphene. Nature, 438,201–204.

115. Dreyer, D.R., Park, S., Bielawski, C.W.,and Ruoff, R.S. (2010) The chemistryof graphene oxide. Chem. Soc. Rev., 39,228–240.

116. Zhu, Y.W., Murali, S., Cai, W.W., Li,X.S., Suk, J.W., Potts, J.R., and Ruoff,R.S. (2010) Graphene and grapheneoxide: synthesis, properties, and appli-cations. Adv. Mater., 22, 3906–3924.

117. Lu, X.K., Yu, M.F., Huang, H., andRuoff, R.S. (1999) Tailoring graphitewith the goal of achieving single sheets.Nanotechnology, 10, 269–272.

118. Li, X.S., Cai, W.W., An, J.H., Kim,S., Nah, J., Yang, D.X., Piner, R.,Velamakanni, A., Jung, I., Tutuc, E.,Banerjee, S.K., Colombo, L., and Ruoff,R.S. (2009) Large-area synthesis ofhigh-quality and uniform graphenefilms on copper foils. Science, 324,1312–1314.

119. Kim, K.S., Zhao, Y., Jang, H., Lee, S.Y.,Kim, J.M., Kim, K.S., Ahn, J.H., Kim, P.,Choi, J.Y., and Hong, B.H. (2009) Large-scale pattern growth of graphene filmsfor stretchable transparent electrodes.Nature, 457, 706–710.

120. Berger, C., Song, Z.M., Li, X.B., Wu,X.S., Brown, N., Naud, C., Mayou, D.,Li, T.B., Hass, J., Marchenkov, A.N.,Conrad, E.H., First, P.N., and de Heer,W.A. (2006) Electronic confinementand coherence in patterned epitaxialgraphene. Science, 312, 1191–1196.

121. Park, S. and Ruoff, R.S. (2009) Chem-ical methods for the production ofgraphenes. Nat. Nanotechnol., 4,217–224.

122. Ren, W.C. and Cheng, H.M. (2014)The global growth of graphene. Nat.Nanotechnol., 9, 726–730.


123. Ferrari, A.C. and Basko, D.M. (2013)Raman spectroscopy as a versatile toolfor studying the properties of graphene.Nat. Nanotechnol., 8, 235–246.

124. Georgakilas, V., Otyepka, M., Bourlinos,A.B., Chandra, V., Kim, N., Kemp, K.C.,Hobza, P., Zboril, R., and Kim, K.S.(2012) Functionalization of graphene:covalent and non-covalent approaches,derivatives and applications. Chem.Rev., 112, 6156–6214.

125. Cai, W.W., Piner, R.D., Stadermann, F.J.,Park, S., Shaibat, M.A., Ishii, Y., Yang,D.X., Velamakanni, A., An, S.J., Stoller,M., An, J.H., Chen, D.M., and Ruoff,R.S. (2008) Synthesis and solid-stateNMR structural characterization of13C-labeled graphite oxide. Science,321, 1815–1817.

126. Gao, W., Alemany, L.B., Ci, L.J., andAjayan, P.M. (2009) New insights intothe structure and reduction of graphiteoxide. Nat. Chem., 1, 403–408.

127. Bekyarova, E., Itkis, M.E., Ramesh, P.,Berger, C., Sprinkle, M., de Heer, W.A.,and Haddon, R.C. (2009) Chemicalmodification of epitaxial graphene:spontaneous grafting of aryl groups. J.Am. Chem. Soc., 131, 1336–1337.

128. Liu, H.T., Ryu, S.M., Chen, Z.Y.,Steigerwald, M.L., Nuckolls, C., andBrus, L.E. (2009) Photochemical reac-tivity of graphene. J. Am. Chem. Soc.,131, 17099–17101.

129. Sofo, J.O., Chaudhari, A.S., andBarber, G.D. (2007) Graphane: a two-dimensional hydrocarbon. Phys. Rev. B,75, 153401.

130. Boukhvalov, D.W., Katsnelson, M.I.,and Lichtenstein, A.I. (2008) Hydro-gen on graphene: electronic structure,total energy, structural distortionsand magnetism from first-principlescalculations. Phys. Rev. B, 77, 035427.

131. Sahin, H., Topsakal, M., and Ciraci,S. (2011) Structures of fluorinatedgraphene and their signatures. Phys.Rev. B, 83, 115432.

132. Elias, D.C., Nair, R.R., Mohiuddin,T.M.G., Morozov, S.V., Blake, P.,

Halsall, M.P., Ferrari, A.C., Boukhvalov,D.W., Katsnelson, M.I., Geim, A.K.,and Novoselov, K.S. (2009) Controlof graphene’s properties by reversiblehydrogenation: evidence for graphane.Science, 323, 610–613.

133. Nair, R.R., Ren, W.C., Jalil, R., Riaz,I., Kravets, V.G., Britnell, L., Blake,P., Schedin, F., Mayorov, A.S., Yuan,S.J., Katsnelson, M.I., Cheng, H.M.,Strupinski, W., Bulusheva, L.G.,Okotrub, A.V., Grigorieva, I.V.,Grigorenko, A.N., Novoselov, K.S.,and Geim, A.K. (2010) Fluorographene:a two-dimensional counterpart ofteflon. Small, 6, 2877–2884.

134. Kashtiban, R.J., Dyson, M.A., Nair,R.R., Zan, R., Wong, S.L., Ramasse, Q.,Geim, A.K., Bangert, U., and Sloan, J.(2014) Atomically resolved imaging ofhighly ordered alternating fluorinatedgraphene. Nat. Commun., 5, 4902.

135. Zhang, L.M., Lu, Z.X., Zhao, Q.H.,Huang, J., Shen, H., and Zhang, Z.J.(2011) Enhanced chemotherapy effi-cacy by sequential delivery of siRNAand anticancer drugs using PEI-graftedgraphene oxide. Small, 7, 460–464.

136. Yang, K., Feng, L.Z., Shi, X.Z., andLiu, Z. (2013) Nano-graphene inbiomedicine: theranostic applications.Chem. Soc. Rev., 42, 530–547.

137. Wang, Y., Li, Z.H., Wang, J., Li, J.H.,and Lin, Y.H. (2011) Graphene andgraphene oxide: biofunctionalizationand applications in biotechnology.Trends Biotechnol., 29, 205–212.

138. Liu, Z., Robinson, J.T., Sun, X.M.,and Dai, H.J. (2008) PEGylatednanographene oxide for delivery ofwater-insoluble cancer drugs. J. Am.Chem. Soc., 130, 10876–10877.

139. Zhang, S.A., Yang, K., Feng, L.Z., andLiu, Z. (2011) In vitro and in vivobehaviors of dextran functionalizedgraphene. Carbon, 49, 4040–4049.

140. Gollavelli, G. and Ling, Y.C. (2012)Multi-functional graphene as an invitro and in vivo imaging probe. Bio-materials, 33, 2532–2545.

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